261663 has 4 divisors (see below), whose sum is σ = 348888. Its totient is φ = 174440.

The previous prime is 261643. The next prime is 261673. The reversal of 261663 is 366162.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 261663 - 2⁵ = 261631 is a prime.

It is a D-number.

It is a zygodrome in base 2.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (261643) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 43608 + ... + 43613.

It is an arithmetic number, because the mean of its divisors is an integer number (87222).

2²⁶¹⁶⁶³ is an apocalyptic number.

261663 is a deficient number, since it is larger than the sum of its proper divisors (87225).

261663 is an equidigital number, since it uses as much as digits as its factorization.

261663 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 87224.

The product of its digits is 1296, while the sum is 24.

The square root of 261663 is about 511.5300577679. The cubic root of 261663 is about 63.9608321541.

The spelling of 261663 in words is "two hundred sixty-one thousand, six hundred sixty-three".